release/src/router/libncurses/ncurses/tty/lib_tstp.c

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  28
  29 /****************************************************************************
  30  *  Author: Zeyd M. Ben-Halim <zmbenhal@netcom.com> 1992,1995               *
  31  *     and: Eric S. Raymond <esr@snark.thyrsus.com>                         *
  32  *     and: Thomas E. Dickey                        1995-on                 *
  33  ****************************************************************************/
  34
  35 /*
  36 **      lib_tstp.c
  37 **
  38 **      The routine _nc_signal_handler().
  39 **
  40 */
  41 #include <curses.priv.h>
  42
  43 #include <SigAction.h>
  44
  45 MODULE_ID("$Id: lib_tstp.c,v 1.48 2014/04/26 18:47:35 juergen Exp $")
  46
  47 #if defined(SIGTSTP) && (HAVE_SIGACTION || HAVE_SIGVEC)
  48 #define USE_SIGTSTP 1
  49 #else
  50 #define USE_SIGTSTP 0
  51 #endif
  52
  53 #ifdef TRACE
  54 static const char *
  55 signal_name(int sig)
  56 {
  57     switch (sig) {
  58 #ifdef SIGALRM
  59     case SIGALRM:
  60         return "SIGALRM";
  61 #endif
  62 #ifdef SIGCONT
  63     case SIGCONT:
  64         return "SIGCONT";
  65 #endif
  66     case SIGINT:
  67         return "SIGINT";
  68 #ifdef SIGQUIT
  69     case SIGQUIT:
  70         return "SIGQUIT";
  71 #endif
  72     case SIGTERM:
  73         return "SIGTERM";
  74 #ifdef SIGTSTP
  75     case SIGTSTP:
  76         return "SIGTSTP";
  77 #endif
  78 #ifdef SIGTTOU
  79     case SIGTTOU:
  80         return "SIGTTOU";
  81 #endif
  82 #ifdef SIGWINCH
  83     case SIGWINCH:
  84         return "SIGWINCH";
  85 #endif
  86     default:
  87         return "unknown signal";
  88     }
  89 }
  90 #endif
  91
  92 /*
  93  * Note: This code is fragile!  Its problem is that different OSs
  94  * handle restart of system calls interrupted by signals differently.
  95  * The ncurses code needs signal-call restart to happen -- otherwise,
  96  * interrupted wgetch() calls will return FAIL, probably making the
  97  * application think the input stream has ended and it should
  98  * terminate.  In particular, you know you have this problem if, when
  99  * you suspend an ncurses-using lynx with ^Z and resume, it dies
 100  * immediately.
 101  *
 102  * Default behavior of POSIX sigaction(2) is not to restart
 103  * interrupted system calls, but Linux's sigaction does it anyway (at
 104  * least, on and after the 1.1.47 I (esr) use).  Thus this code works
 105  * OK under Linux.  The 4.4BSD sigaction(2) supports a (non-portable)
 106  * SA_RESTART flag that forces the right behavior.  Thus, this code
 107  * should work OK under BSD/OS, NetBSD, and FreeBSD (let us know if it
 108  * does not).
 109  *
 110  * Stock System Vs (and anything else using a strict-POSIX
 111  * sigaction(2) without SA_RESTART) may have a problem.  Possible
 112  * solutions:
 113  *
 114  *    sigvec      restarts by default (SV_INTERRUPT flag to not restart)
 115  *    signal      restarts by default in SVr4 (assuming you link with -lucb)
 116  *                and BSD, but not SVr3.
 117  *    sigset      restarts, but is only available under SVr4/Solaris.
 118  *
 119  * The signal(3) call is mandated by the ANSI standard, and its
 120  * interaction with sigaction(2) is described in the POSIX standard
 121  * (3.3.4.2, page 72,line 934).  According to section 8.1, page 191,
 122  * however, signal(3) itself is not required by POSIX.1.  And POSIX is
 123  * silent on whether it is required to restart signals.
 124  *
 125  * So.  The present situation is, we use sigaction(2) with no
 126  * guarantee of restart anywhere but on Linux and BSD.  We could
 127  * switch to signal(3) and collar Linux, BSD, and SVr4.  Any way
 128  * we slice it, System V UNIXes older than SVr4 will probably lose
 129  * (this may include XENIX).
 130  *
 131  * This implementation will probably be changed to use signal(3) in
 132  * the future.  If nothing else, it's simpler...
 133  */
 134
 135 #if USE_SIGTSTP
 136 static void
 137 handle_SIGTSTP(int dummy GCC_UNUSED)
 138 {
 139     SCREEN *sp = CURRENT_SCREEN;
 140     sigset_t mask, omask;
 141     sigaction_t act, oact;
 142
 143 #ifdef SIGTTOU
 144     int sigttou_blocked;
 145 #endif
 146
 147     _nc_globals.have_sigtstp = 1;
 148     T(("handle_SIGTSTP() called"));
 149
 150     /*
 151      * The user may have changed the prog_mode tty bits, so save them.
 152      *
 153      * But first try to detect whether we still are in the foreground
 154      * process group - if not, an interactive shell may already have
 155      * taken ownership of the tty and modified the settings when our
 156      * parent was stopped before us, and we would likely pick up the
 157      * settings already modified by the shell.
 158      */
 159     if (sp != 0 && !sp->_endwin)        /* don't do this if we're not in curses */
 160 #if HAVE_TCGETPGRP
 161         if (tcgetpgrp(STDIN_FILENO) == getpgrp())
 162 #endif
 163             NCURSES_SP_NAME(def_prog_mode) (NCURSES_SP_ARG);
 164
 165     /*
 166      * Block window change and timer signals.  The latter
 167      * is because applications use timers to decide when
 168      * to repaint the screen.
 169      */
 170     (void) sigemptyset(&mask);
 171 #ifdef SIGALRM
 172     (void) sigaddset(&mask, SIGALRM);
 173 #endif
 174 #if USE_SIGWINCH
 175     (void) sigaddset(&mask, SIGWINCH);
 176 #endif
 177     (void) sigprocmask(SIG_BLOCK, &mask, &omask);
 178
 179 #ifdef SIGTTOU
 180     sigttou_blocked = sigismember(&omask, SIGTTOU);
 181     if (!sigttou_blocked) {
 182         (void) sigemptyset(&mask);
 183         (void) sigaddset(&mask, SIGTTOU);
 184         (void) sigprocmask(SIG_BLOCK, &mask, NULL);
 185     }
 186 #endif
 187
 188     /*
 189      * End window mode, which also resets the terminal state to the
 190      * original (pre-curses) modes.
 191      */
 192     NCURSES_SP_NAME(endwin) (NCURSES_SP_ARG);
 193
 194     /* Unblock SIGTSTP. */
 195     (void) sigemptyset(&mask);
 196     (void) sigaddset(&mask, SIGTSTP);
 197 #ifdef SIGTTOU
 198     if (!sigttou_blocked) {
 199         /* Unblock this too if it wasn't blocked on entry */
 200         (void) sigaddset(&mask, SIGTTOU);
 201     }
 202 #endif
 203     (void) sigprocmask(SIG_UNBLOCK, &mask, NULL);
 204
 205     /* Now we want to resend SIGSTP to this process and suspend it */
 206     act.sa_handler = SIG_DFL;
 207     sigemptyset(&act.sa_mask);
 208     act.sa_flags = 0;
 209 #ifdef SA_RESTART
 210     act.sa_flags |= SA_RESTART;
 211 #endif /* SA_RESTART */
 212     sigaction(SIGTSTP, &act, &oact);
 213     kill(getpid(), SIGTSTP);
 214
 215     /* Process gets suspended...time passes...process resumes */
 216
 217     T(("SIGCONT received"));
 218     sigaction(SIGTSTP, &oact, NULL);
 219     NCURSES_SP_NAME(flushinp) (NCURSES_SP_ARG);
 220
 221     /*
 222      * If the user modified the tty state while suspended, he wants
 223      * those changes to stick.  So save the new "default" terminal state.
 224      */
 225     NCURSES_SP_NAME(def_shell_mode) (NCURSES_SP_ARG);
 226
 227     /*
 228      * This relies on the fact that doupdate() will restore the
 229      * program-mode tty state, and issue enter_ca_mode if need be.
 230      */
 231     NCURSES_SP_NAME(doupdate) (NCURSES_SP_ARG);
 232
 233     /* Reset the signals. */
 234     (void) sigprocmask(SIG_SETMASK, &omask, NULL);
 235 }
 236 #endif /* USE_SIGTSTP */
 237
 238 static void
 239 handle_SIGINT(int sig)
 240 {
 241     SCREEN *sp = CURRENT_SCREEN;
 242
 243     /*
 244      * Much of this is unsafe from a signal handler.  But we'll _try_ to clean
 245      * up the screen and terminal settings on the way out.
 246      *
 247      * There are at least the following problems:
 248      * 1) Walking the SCREEN list is unsafe, since all list management
 249      *    is done without any signal blocking.
 250      * 2) On systems which have REENTRANT turned on, set_term() uses
 251      *    _nc_lock_global() which could deadlock or misbehave in other ways.
 252      * 3) endwin() calls all sorts of stuff, many of which use stdio or
 253      *    other library functions which are clearly unsafe.
 254      */
 255     if (!_nc_globals.cleanup_nested++
 256         && (sig == SIGINT || sig == SIGTERM)) {
 257 #if HAVE_SIGACTION || HAVE_SIGVEC
 258         sigaction_t act;
 259         sigemptyset(&act.sa_mask);
 260         act.sa_flags = 0;
 261         act.sa_handler = SIG_IGN;
 262         if (sigaction(sig, &act, NULL) == 0)
 263 #else
 264         if (signal(sig, SIG_IGN) != SIG_ERR)
 265 #endif
 266         {
 267             SCREEN *scan;
 268             for (each_screen(scan)) {
 269                 if (scan->_ofp != 0
 270                     && NC_ISATTY(fileno(scan->_ofp))) {
 271                     scan->_outch = NCURSES_SP_NAME(_nc_outch);
 272                 }
 273                 set_term(scan);
 274                 NCURSES_SP_NAME(endwin) (NCURSES_SP_ARG);
 275                 if (sp)
 276                     sp->_endwin = FALSE;        /* in case of reuse */
 277             }
 278         }
 279     }
 280     _exit(EXIT_FAILURE);
 281 }
 282
 283 #if USE_SIGWINCH
 284 static void
 285 handle_SIGWINCH(int sig GCC_UNUSED)
 286 {
 287     _nc_globals.have_sigwinch = 1;
 288 # if USE_PTHREADS_EINTR
 289     if (_nc_globals.read_thread) {
 290         if (!pthread_equal(pthread_self(), _nc_globals.read_thread))
 291             pthread_kill(_nc_globals.read_thread, SIGWINCH);
 292         _nc_globals.read_thread = 0;
 293     }
 294 # endif
 295 }
 296 #endif /* USE_SIGWINCH */
 297
 298 /*
 299  * If the given signal is still in its default state, set it to the given
 300  * handler.
 301  */
 302 static int
 303 CatchIfDefault(int sig, void (*handler) (int))
 304 {
 305     int result;
 306 #if HAVE_SIGACTION || HAVE_SIGVEC
 307     sigaction_t old_act;
 308     sigaction_t new_act;
 309
 310     memset(&new_act, 0, sizeof(new_act));
 311     sigemptyset(&new_act.sa_mask);
 312 #ifdef SA_RESTART
 313 #ifdef SIGWINCH
 314     if (sig != SIGWINCH)
 315 #endif
 316         new_act.sa_flags |= SA_RESTART;
 317 #endif /* SA_RESTART */
 318     new_act.sa_handler = handler;
 319
 320     if (sigaction(sig, NULL, &old_act) == 0
 321         && (old_act.sa_handler == SIG_DFL
 322             || old_act.sa_handler == handler
 323 #if USE_SIGWINCH
 324             || (sig == SIGWINCH && old_act.sa_handler == SIG_IGN)
 325 #endif
 326         )) {
 327         (void) sigaction(sig, &new_act, NULL);
 328         result = TRUE;
 329     } else {
 330         result = FALSE;
 331     }
 332 #else /* !HAVE_SIGACTION */
 333     void (*ohandler) (int);
 334
 335     ohandler = signal(sig, SIG_IGN);
 336     if (ohandler == SIG_DFL
 337         || ohandler == handler
 338 #if USE_SIGWINCH
 339         || (sig == SIGWINCH && ohandler == SIG_IGN)
 340 #endif
 341         ) {
 342         signal(sig, handler);
 343         result = TRUE;
 344     } else {
 345         signal(sig, ohandler);
 346         result = FALSE;
 347     }
 348 #endif
 349     T(("CatchIfDefault - will %scatch %s",
 350        result ? "" : "not ", signal_name(sig)));
 351     return result;
 352 }
 353
 354 /*
 355  * This is invoked once at the beginning (e.g., from 'initscr()'), to
 356  * initialize the signal catchers, and thereafter when spawning a shell (and
 357  * returning) to disable/enable the SIGTSTP (i.e., ^Z) catcher.
 358  *
 359  * If the application has already set one of the signals, we'll not modify it
 360  * (during initialization).
 361  *
 362  * The XSI document implies that we shouldn't keep the SIGTSTP handler if
 363  * the caller later changes its mind, but that doesn't seem correct.
 364  */
 365 NCURSES_EXPORT(void)
 366 _nc_signal_handler(int enable)
 367 {
 368     T((T_CALLED("_nc_signal_handler(%d)"), enable));
 369 #if USE_SIGTSTP                 /* Xenix 2.x doesn't have SIGTSTP, for example */
 370     {
 371         static bool ignore_tstp = FALSE;
 372
 373         if (!ignore_tstp) {
 374             static sigaction_t new_sigaction, old_sigaction;
 375
 376             if (!enable) {
 377                 new_sigaction.sa_handler = SIG_IGN;
 378                 sigaction(SIGTSTP, &new_sigaction, &old_sigaction);
 379             } else if (new_sigaction.sa_handler != SIG_DFL) {
 380                 sigaction(SIGTSTP, &old_sigaction, NULL);
 381             } else if (sigaction(SIGTSTP, NULL, &old_sigaction) == 0
 382                        && (old_sigaction.sa_handler == SIG_DFL)) {
 383                 sigemptyset(&new_sigaction.sa_mask);
 384 #ifdef SA_RESTART
 385                 new_sigaction.sa_flags |= SA_RESTART;
 386 #endif /* SA_RESTART */
 387                 new_sigaction.sa_handler = handle_SIGTSTP;
 388                 (void) sigaction(SIGTSTP, &new_sigaction, NULL);
 389             } else {
 390                 ignore_tstp = TRUE;
 391             }
 392         }
 393     }
 394 #endif /* !USE_SIGTSTP */
 395
 396     if (!_nc_globals.init_signals) {
 397         if (enable) {
 398             CatchIfDefault(SIGINT, handle_SIGINT);
 399             CatchIfDefault(SIGTERM, handle_SIGINT);
 400 #if USE_SIGWINCH
 401             CatchIfDefault(SIGWINCH, handle_SIGWINCH);
 402 #endif
 403             _nc_globals.init_signals = TRUE;
 404         }
 405     }
 406     returnVoid;
 407 }